GTO HAS A LOW IDLE, CANNOT HOLD

1970 Pontiac Other

1970 Pontiac GTO V8 Two Wheel Drive Automatic Unknown miles

My car cannot seem to stay running for more than a few seconds after ignition. A slight hissing sound is heard from the engine, and every new startup needs a few pumps of the throttle to get enough gas into the carburetor. It idles ok for a few seconds, but will putter out within seconds.